FIG. 1 (Prior Art) is an exploded perspective view of an assembly involving one type of fluorescent lamp fixture referred to here as an old-fashioned or a “legacy” fluorescent lamp fixture. FIG. 2 (Prior Art) is a circuit schematic of the assembly of FIG. 1. Legacy fixture 1 includes a base portion 2, a transparent cover or lens 3, and a starter unit 5. Base portion 2 of the fixture includes a pair of T8 lamp holders 6 and 7, a starter socket 8, a magnetic ballast 9 that is disposed under a removable metal cover or tent 10, and other parts not shown. A fluorescent lamp 4 is installed in the fixture. Fixture 1 receives AC power via electrical cord 11. In one example, the fluorescent lamp 4 is a so-called T8 tubular fluorescent lamp having opposing G13 bi-pin bases 12 and 13. The T8 lamp is installed in the fixture so that the two pins of G13 bi-pin base 12 fit into lamp holder 6 and make contact with two corresponding electrical contacts in lamp holder 6. Similarly, the two pins of G13 bi-pin base 13 fit into lamp holder 7 and make contact with two corresponding electrical contacts in lamp holder 7. When starter unit 5 is installed, the two terminals of the starter unit fit up and into corresponding holes in starter socket 8 and make electrical connections to two corresponding electrical contacts in the socket.
As is known in the art, a starter unit is required to turn on the lamp. In a first step, when AC power is applied to the fixture via cord 11, a switch in starter unit 5 closes and forms an electrical connection between the filament 14 at one end of lamp 4 and the filament 15 at the other end of lamp 4. An alternating current can then flow from an AC power source 16, through inductive ballast 9, through filament 14, through the closed switch of the starter unit 5, and through the second filament 15, and back to the AC power source 16. This flow of this current causes the filaments to heat. The heating of the filaments causes gas surrounding the filaments to ionize. Once the gas is ionized in this way, then the switch in the starter unit is opened. The opening of the switch cuts current flow through magnetic ballast 9, thereby causing a large voltage spike to develop due to the inductive nature of the ballast. Due to the circuit topology, this large voltage is present between filaments 14 and 15. The voltage is large enough to strike an arc between the filaments through the gas within the lamp. Once the arc is established, the resistance between the two filaments through the gas decreases. This allows current to continue to flow through the gas without a large voltage being present between the filaments. The switch of the starter unit is left open, the current continues to flow, filaments continue to be heated, the arc is maintained, and the magnitude of current flow is limited by the ballast. The fluorescent lamp is then said to be on. The arc generates UV light that then strikes a phosphor coating on the inside surface of the glass of the lamp. The phosphor coating captures energy of the UV light and reemits visible light.
FIG. 3 (Prior Art) is a circuit diagram of an assembly involving another type of fluorescent lamp fixture 20. This type of fixture employs an electronic ballast 21. Due to the operation of the electronic ballast, no separate starter unit is provided. Wires 23-26 and lamp holders 27 and 28 are parts of the fixture. Electronic ballast 21 receives 50-60 Hz AC power from AC source 16, and then supplies a T8 fluorescent lamp 22 with an AC power signal having a higher frequency (for example, 20 kHz). Fluorescent lamps are generally more efficient in terms of converting electrical energy into visible light when they are driven at a higher frequency such as 20 kHz as opposed to when they are driven with an AC signal at 50-60 Hz. For these and other reasons, new fluorescent lamps fixtures are generally of the electronic ballast type. Legacy type fixtures as shown in FIG. 1 still exist, but generally are older fixtures that have been installed and in use for some time.
FIG. 4 (Prior Art) is a circuit diagram of an assembly in which a so-called “T8-to-T5 retrofit assembly” 30 has been installed in a legacy fluorescent lamp fixture. The T8-to-T5 retrofit assembly 30 has the approximate form factor of an ordinary T8 fluorescent lamp. In this form factor, the T8-to-T5 retrofit assembly 30 provides two G13 bi-pin bases 31 and 32 mounted in opposing fashion as illustrated so that the T8-to-T5 retrofit assembly 30 can be installed in lamp holders 33 and 34 in place of a T8 lamp. In addition, retrofit assembly 30 includes an electronic ballast 35, a T5 fluorescent lamp 36, and two T5 lamp holders 37 and 38 configured to hold the T5 lamp. The electronic ballast 35 receives 50-60 Hz AC power from AC source 16. A first conductive path extends from AC source 16, through ballast 39, through wire 40 of the legacy fixture, through contact 41 of lamp holder 33, and into the T8-to-T5 retrofit assembly, and to a first power input of electronic ballast 35. A second conductive path extends from AC source 16, through wire 42 of the legacy fixture, through contact 43 of lamp holder 34, into the T8-to-T5 retrofit assembly, through a short connection 44 within the retrofit assembly, back out of the T8-to-T5 retrofit assembly via contact 54 of lamp holder 34, through wire 45 of the legacy fixture, through a dummy short 46 that is installed in starter socket 47, through wire 48 of the legacy fixture, through contact 49 of lamp holder 33, back into the retrofit assembly, and to a second power input of electronic ballast 35. The electronic ballast receives AC power through these two conductive paths. The electronic ballast drives the T5 fluorescent lamp 36 via four conductors 50-53. The existence of magnetic ballast 39 in the AC current path between AC source 16 and electronic ballast 35 does not interfere with operation of the electronic ballast. The magnetic ballast is of such an inductance that at the low 50-60 Hz frequency of the incoming AC power signal, the magnetic ballast has only a small impedance. By replacing a T8 lamp of a legacy fixture with such a T8-to-T5 retrofit assembly, power savings due to more efficient operation of the lamp can be realized. The fact that the smaller T5 lamp may output less light than the original larger T8 lamp is generally acceptable considering the improved efficiency gained.
FIG. 5 (Prior Art) is a circuit diagram of a proposed circuit whereby an owner of a legacy fixture 55 can achieve even more power savings as compared to using the circuit of FIG. 4. In the assembly of FIG. 5, an RF-enabled switch 56 is provided in the starter unit socket 57 of the legacy fixture. The internal wiring of the legacy fixture of the circuit of FIG. 5 is identical to the internal wiring of the legacy fixture of FIG. 1. The T8-to-T5 retrofit assembly 61 of FIG. 5 is identical to the T8-to-T5 retrofit assembly 30 of FIG. 4. The legacy fixture is generally a fixture that has been installed and used with T8 bulbs for many years, and is now being retrofitted to improve efficiency.
In the assembly of FIG. 5, the circuitry of the RF-enabled switch 56 receives power via existing conductors 58 and 59 of the legacy fixture. A switch in the RF-enabled switch 56 can be made to open in response to receiving an RF control signal 60. If the switch is open, then power to the retrofit assembly 61 is cut off, lamp 62 is therefore off and is not powered. The switch in the RF-enabled switch 56 can also be made to close in response to receiving another RF control signal 63. If the switch is closed, then power is supplied through the RF-enabled switch 56 and to the retrofit assembly 61. The retrofit assembly 61 responds in standard fashion and drives lamp 62 so that lamp 62 is illuminated. By turning the lamp off when light is not needed, additional power savings can be realized in addition to the power savings achieved by simple use of the retrofit assembly.
In one example, the circuit of FIG. 5 is installed in a room. A remotely located infra-red occupancy detector circuit (not shown) detects whether there are people in the room. If no people are detected and it is determined that light from lamp 62 is not needed, then the infra-red occupancy detector circuit transmits RF control signal 60 to the RF-enabled switch 56 thereby causing lamp 62 to be turned off. If, however, people are detected to be in the room, then the infra-red occupancy detector circuit may transmit RF control signal 63 to the RF-enabled switch 56 thereby causing lamp 62 to be turned on. By keeping the lamp 62 off when it is not needed, the circuit of FIG. 5 achieves additional power savings as compared to the circuit of FIG. 4.